Project Summary/Abstract The incidence of chronic kidney disease (CKD) is increasing due to the ever-expanding number of people who are either obese (33%) or diabetic (9%) or both. In a significant proportion of obese-diabetic subjects, CKD may progress to end stage renal disease (ESRD) and dialysis faster than non-obese diabetic subjects. Care of ESRD patients (1% of Medicare population) consumes Medicare dollars in a disproportional manner (7%). Hence, preventing progression of CKD to ESRD is of paramount importance. Currently, the standard of care is to use medications that block/suppress activation of the renin-angiotensin system. However, these medications are not enough to stop progression to ESRD in many subjects and novel therapeutic agents are needed. DPP4 inhibitors are conveniently placed at the intersection of diabetes and CKD due to recent data showing improvement in proteinuria in diabetic patients with CKD (SAVOR-TIMI trial and animal models). Dr. Nistala and others have shown that DPP4 inhibitors may have kidney specific effects independent of blood pressure or blood sugar improvement. However, the mechanisms of DPP4 inhibitor-mediated benefits in the kidney are relatively unknown. If DPP4 inhibitors are to be used for preventing progression of kidney disease, the biological function of DPP4 in the kidney needs better understanding. Data supports the notion that DPP4 may regulate sodium absorption and albumin/oligomeric peptide endocytosis in proximal tubules of the kidney. In addition, DPP4 is a co-stimulatory molecule for T-lymphocytes, activates mononuclear cells (including macrophages and antigen presenting cells [APCs]) and may mediate inflammation based on findings from fat depots in obese and plasma from diabetes patients. Tubulointerstitial inflammation and fibrosis plays an important role in the progression of CKD in the setting of obesity and diabetes and importantly, Dr. Nistala found that DPP4 activity is increased in the kidney and expression levels are higher in the proximal tubules of obese/diabetic mice. Therefore, this project is focused on examining the role of DPP4 in the proximal tubule and kidney immune system in the setting of obesity/diabetes. The experiments are designed to address the central hypothesis that obesity- induced proximal tubule DPP4 activation incites a pro-inflammatory immune response leading to tubulointerstitial fibrosis and progression of kidney disease. To address this hypothesis, DPP4 will be activated via high sucrose/high fat (Western Diet) feeding in mice with or without DPP4 deficiency. In Aim 1, the role of Western diet in activation of DPP4 in the proximal tubule and tubular dysfunction will be studied by using proximal tubule specific deletion of DPP4. In Aim 2, the role of proximal tubule DPP4 in kidney immune system activation will be examined. In Aim 3, the role of proximal tubule DPP4-induced immune system activation in tubulointerstitial fibrosis and kidney disease progression will be studied. It is anticipated that results from this project will yield unique insights into the mechanisms of kidney injury and inflammation in obesity/diabetes with the ultimate goal of translating these findings into meaningful treatments.